You are basically right. The bolded parts are the key.
Councell is a prototypical DOG. Ishaq Williams is a prototypical CAT. The DOG should be a bit faster, with cover skills a priority, and the CAT should be a bit stronger, with pass-rush skills a priority, but ideally they will be somewhat interchangeable so that the defense can't tell what's coming by what personnel is where. Both guys should be essentially long, fast and strong, able to rush the passer on one play and drop back in coverage on the next.
Shembo doesn't fit profile for us at OLB at all, whether DOG or CAT. He's built like an ILB, and he was listed at ILB when he started. If I'm not mistaken, he was rated as an ILB by recruiting services coming out of high school.
But again, what that tells you is that profile isn't everything. Shembo is shorter and stubbier than we'd like at his position, but he is such a relentless, explosive, powerful pass rusher that he has beaten out Ishaq at CAT for 2 years now.
And I wouldn't be stunned if Kolin Hill is able to pull off a similar feat.